1. Field of the Invention
The present invention is directed to audio conferencing systems, and more particularly to a method of discriminating between a single talker with an acoustic reflection and two talkers regardless of their power levels.
2. Description of the Related Art
In hands-free audio conferencing systems, acoustic reflections from the walls cause reverberations that deteriorate the audio quality. This phenomenon is commonly known as the barrel effect.
Microphone arrays and beamforming techniques can be used to solve this problem by capturing the sound originating from a desired direction and attenuating the sounds originating from all other directions. However, simple microphone arrays cannot discriminate between the case of a single talker with a strong acoustic reflection and the case of two different talkers.
This problem is more serious when azimuth data from the microphone array is used for non-audio purposes, for example, to steer a video camera in a video conferencing system. If the microphone array mistakenly interprets a reflection as a second talker, the camera will point to the wall, post, or column that caused the reflection. This scenario is common when a talker looks to another participant in the conference instead of looking at the microphone array, resulting in a reflected audio signal that is stronger than the direct path signal. This, in turn, leads to an incorrect localization by the array.
Most audio systems require the talkers to be as close as possible to the microphones so that the direct path signal is significantly stronger than the reflections. In applications where the location of the desired audio signal is known and fixed, directional microphones are usually used. In other applications where the location of the desired audio signal is not known and/or is dynamic, a microphone array, either of switched directional microphones or omnidirectional microphones equipped with a beamforming algorithm is usually used to locate and track the desired audio signal.
A number of different approaches have been proposed to solve this problem [see F. Beaucoup, M. Tetelbaum, Robust Talker Localization in Reverberant Environment, U.S. patent application 20030051532, Mar. 20, 2003; A. Maziar; D. Schulz, M. Tetelbaum, Acoustic talker localization, U.S. patent application 20020001389, Jan. 3, 2002; and C. H. Coker, D. R. Fishell, Acoustic direction Identification System, U.S. Pat. No. 4,581,758, Apr. 8, 1986]. Other approaches include the use of near-field beam forming techniques to restrict the detection capability of the microphone array to a given distance from the array, thus reducing the magnitude of the acoustic reflections.